AS2: support polls

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API docs: entities, endpoints. would need to figure out how to represent them in AS1.

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looks like this would be objectType question in AS1:

Represents a question or a poll. Objects of this type MAY contain an additional options property whose value is an Array of possible answers to the question in the form of Activity Stream objects of any type.

...and type Question in AS2:

The Question object can be used to express various types of inquiries. For instance, simple open-ended questions similar to those posted to crowd-sourced question and answer websites...Multiple-choice questions or "polls" are also supported using either the oneOf or anyOf properties.

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This might be higher priority now that we're rendering Mastodon posts in Bridgy Fed feeds.

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Remaining work here is rendering in HTML and plain text, ie AS1 => HTML, RSS, Atom, JSON Feed.

Example post:

• https://tech.lgbt/@nelson/110101971009516952
• https://granary.io/url?input=as2&output=as1&url=https%3A%2F%2Ftech.lgbt%2F%40nelson%2F110101971009516952

[snarfed]

The quick and dirty path here would be to add this to microformats2.render_content. The deeper path would be to figure out the mf2 for polls, add that to microformats2.object_to_json, then add the HTML rendering to json_to_html. I'd probably be ok with either.